1. Field of the Invention
The present invention relates to electrode structures including transparent electrode structures, in particular self supporting electrode structures. Further, applications of the herein novel electrode structures are provided, including electronic writing tablets, electronic paper and fabrication methods for electronic writing tablets and electronic paper.
2. Description of the Related Art
Countless electrode structures have been developed and applied over time. However, transparent electrodes have been limited in their development primarily due to material limitations. Transparent electrode materials have been primarily based on tin oxide, indium-tin-oxide, zinc oxide, or conductive polymers. However, such materials are known to be transparent conductors only if certain special conditions are met in their preparation, and if their thicknesses are less than 5000 Angstroms. Thus, bulk glass or plastic substrates are required to impart mechanical strength.
For the past decades, much widespread discussion, publicity and speculation has been directed towards a paperless society. Benefits of such a society include minimization of deforesting and refuse. Further, paper processing involves usage of many environmentally harsh chemicals, generally to bleach the paper.
Additionally, although ubiquitous for hundreds of years, newspapers themselves have many drawbacks. The inks used commonly rub off, making reading a newspaper a messy event due to ink transfer from the paper to individuals' hands.
Accordingly, to this end, there have been proposed various “paper-like” displays, which generally have stylus input and display functionality.
Liquid crystal material has been used, for example, as is known in conventional LCDs having pen-based input (e.g., see T. Ogawa et al., “The Trends of reflective LCDs for future electronic paper”, SID '98 Digest, p. 217) However, such conventional LCD based are generally bulky and require relatively high operating voltage to overcome the resistance imparted by conventional LCD display protective substrates.
There has recently been a number of proposed soltuions using MEM (microelectromechanical) devices for display applications. Two types of MEM based direct view displays have been proposed. In one (See e.g., E. Stem, “Large-area micromechanical flat-panel display”, SID 97 Digest, p. 230), an array of passively addressed bistable transparent beams are used to control the release of light trapped by total internal reflection. This device, however, requires a complicated backlighting system, and is not suitable for portable electronic writing tablets. Further, protective substrates increase bulk and requisite operating voltage.
A second type uses micromachined deformable optical cavities whose reflected color changes with voltage. (See e.g., M. W. Miles, “A new reflective FPD technology using interferrometric modulation”, SID 97 Digest (1997) p.71). Again, however, protective substrates increase bulk and requisite operating voltage.
Other types of displays, referred to as “electroscopic displays”, use an electroscopic fluid display where a plate or grid which is reflective and movable is sealed with a glass plate and filled with a nonconducting colored solvent. If the penetration depth of the incident light in the solvent is much smaller than the cell thickness, than when the reflective grid is located near the bottom plate, the grid will not be visible and the solvent color will be visible. However, when the reflective grid is attracted to the front side, the reflective grid will be visible and the cell will appear white. Such systems are described, for example, in Te Velde et al., “A family of electroscopic displays”, Society of Information Display 1980 technical digest, p.116-117 and the following U.S. Pat. Nos. 4,178,077, 4,519,676, 4,729,636.). These systems require complex structures of springy capacitors or triodes which must control physical movement of the grid.
Also proposed are displays integrating addressing electronics on the display itself to reduce cost and improve yield. For an 8½ by 11 inch display, approximately 1,275 gate line and about 1,650 data line connections and driver chip outputs are needed. These systems are described by J. L. Sanford et al. in “Silicon light valve array chip for high resolution reflective liquid crystal projection displays”, IBM J. Res. Develop., Vol. 42 No. 3/4, May/Jun. 1998, pp.347-358.
Flexible electronic paper systems have also been proposed. Prominent in the endeavor to develop flexible electronic paper systems are E Ink and Gyricon.
E Ink Corporation (Cambridge, Mass.) provides an “electronic ink” system whereby millions of tiny microcapsules, about 100 microns in diameter, are provided between substrates. The microcapsules contain positively charged white particles and negatively charged black particles suspended in a clear fluid. When a negative electric field is applied, the white particles move to the top of the microcapsule where they become visible to the user, and an opposite electric field pulls the black particles to the bottom of the microcapsules where they are hidden. The process is reversible whereby the black particles appear at the top of the capsule.
Gyricon LLC (Ann Arbor, Mich.) teaches a reusable display material known as SmartPaper™ that is electrically writable and erasable. This system is disclosed, e.g., in U.S. Pat. No. 4,126,854 entitled “Twisting ball panel display” to Nicholas Sheridon. The technology uses an array of solid beads about 100 micron diameter or smaller, with one hemisphere of each bead one color (e.g. white) and the other a different color (e.g. black). The beads are embedded in a flexible plastic sheet in small cavities surrounded by a liquid. Each bead carries an electrical charge. Upon application of an external electric field the bead rotates when adhesive forces between each bead and the cavity wall are overcome by a requisite electrical threshold. This displays an image electrically on the material, and is erasable with another transmission. Electrical signals can be applied through fixed surface electrodes or a moving stylus.
An ideal electronic paper media desirably has the following characteristics:                physical resemblance to conventional paper, in the form of sheets, notebooks or tablets with multiple pages, poster boards, or other known paper types;        inexpensive to manufacture, making electronic paper ubiquitous;        flexibility such that pages of electronic paper may readily be turned, similar to pages in a notebook;        low operating voltage, thereby decreasing weight and bulk in portable systems by reducing battery or other power source weight and bulk.        
As discussed above, no existing liquid crystal based systems meet these ideal systems. They typically require many discreet and precise manufacturing steps for acceptable electronic writing tablets, increasing cost and limiting the market to high end users. Many of the above described systems are limited by bulk and rigidity. A major problem among all or most convention electronic paper or tablet systems is that the transparent conductive materials are not self supporting, and require substantial mechanical support. Tin oxide, indium-tin-oxide, zinc oxide, or conductive polymers are known to be transparent conductors if certain special conditions are met in their preparation and if their thicknesses are less than 5000 Angstroms. Thus, bulk glass or plastic substrates are required to impart mechanical strength. This adds, in addition to bulk and weight, resistance, increasing requisite operating voltage, and hence creating a need for expensive and bulky driver systems. Further, these substrates decrease resolution, generally a function of glass or plastic thickness. They do not resemble regular paper. Conventional electronic paper systems are typically bulky, expensive to manufacture, high voltage requiring expensive drivers, etc.